UGVs are motorized vehicles that operate without an on-board human presence. Remotely-controlled and remotely-guided unmanned vehicles (such as UGVs) are in widespread use in applications such as Explosive Ordinance Disposal (“EOD”), search and rescue operations, hazardous material disposal, surveillance, etc. A typical UGV includes a chassis, wheels, drive motors mounted on the chassis, an articulating arm mounted on top of the chassis, grippers and a camera mounted on the arm. UGVs can also be equipped with steerable front wheels to facilitate directional control. Alternatively, UGVs can include tracks that facilitate operation over rough terrain. Steering of tracked UGVs can be effectuated by simultaneously operating the wheels or tracks on opposite sides of the UGV.
Movement and steering of an UGV can be controlled by a user from a location remote from the UGV using a joystick-equipped control unit. The control unit communicates with the UGV by way of a wireless communication link or a tether communication link. The control unit may also be used to remotely control the UGV's robotic arm, gripper, and camera. Movement of the UGV is typically controlled by modulating the velocity of the UGV in proportion to the displacement of the joystick of the control unit.
The tether communication link is used when Radio Frequency (“RF”) communication is not possible or not preferred. For example, the tether communication link is used when the UGV is operating in an RF-denied environment (e.g., jamming), in a difficult RF environment (e.g., underground tunnels), or in a scenario in which it is desirable to minimize RF signature (e.g., to avoid detection).
The tether communication link is typically implemented via a Fiber-Optic (“F/O”) cable. The tether media is paid out from a spool. Spool pay-out is controlled. Re-usable tether media is re-wound onto the spool after use. This type of spooling mechanism requires the use of a spool drag device to control tether tension during pay-out. It is extremely difficult to achieve consistent drag (due to effects of temperature, humidity, dust, etc.). Incorrect drag performance can foul the spool, compromising the mission.
There are two types of tether spools, namely a single use tether spool and a multi-use tether spool. The single use tether spool has a simple design with no drag mechanism. However, the single use tether spool is not reusable, and therefore is an expensive solution. The multi-use tether spool is reusable, and therefore has a lower lifetime cost as compared to the single user tether spool. However, the multi-use tether spool is more complex (e.g., it may require a level-wind mechanism) and experiences spool fouling if drag is not applied correctly.